Frequency synthesizer having first phase locked loop frequency multiplied by near unity in second phase locked loop

Abstract

A Frequency synthesis stage comprises two phase locked loops. The first (O 1 , D 1 , M, CP 1 , D 2 ) divides the frequency Fo+Δ derived from preceding stages by N/Q, N being a variable integer, and adds to the result a standard frequency P which is in a fixed ratio with a value representative of large frequency steps so as to give an intermediate frequency F A , while the second (O 2 , M 0 , M 1 , CP 2 D 3 ) multiplies F A by NQ/r. P and Q are selected so that the product PQ is approximately equal to the mean of the limit values desired for the output frequency.

What is claimed is: 
     
       1. A frequency synthesizer for generating an output frequency variable in a predetermined range by frequency steps having a predetermined value, said synthesizer comprising a first phase locked loop including a first current or voltage controlled oscillator, said first oscillator having a frequency control input and an ouput; a first phase comparator having first and second inputs and an output, the output of the first comparator being connected to the frequency control input of the first oscillator, source means providing an input frequency (F o  +Δ), F o  being a fixed frequency and Δ being a frequency increment variable by predetermined steps which are small with respect to the steps of variation of the output frequency; first divider means connecting said source means to the first input of the first comparator, said first divider means having a first programmable division factor N which is adapted to take a first number of values equalling the number of steps of variation in said output frequency range; second divider means and first mixer means serially connected between the output of the first oscillator and the second input of the first comparator, said second divider means having a second predetermined factor of division Q and a source of standard frequency connected to the first mixer means, said frequency synthesizer further comprising a second phase locked loop including a second current or voltage controlled oscillator having a frequency control input and an output on which the output frequency of the synthesizer is generated, a second phase comparator having first and second inputs and an output, the output of the second phase comparator being connected to the frequency control input of the second oscillator; second mixer means having first and second inputs and an output, the first and second inputs of the second mixer means being respectively connected to the respective outputs of the first and second oscillators, and circuit means connecting the output of the second mixer means to the first input of the second phase comparator and the output of the first oscillator to the second input of the second phase comparator, said circuit means comprising a third frequency divider having a third predetermined division factor R, an input connected to the output of said first oscillator and output means connected to the second input of the second phase comparator, and means connecting the output of the second mixer means to the first input of the second phase comparator, the first and second factors N and Q and the standard frequency having such values that the output frequency F A   of the first oscillator is located within the predetermined range of the output frequency. 
     
     
       2. A frequency synthesizer as claimed in claim 1, wherein the first division factor N has such values that the ratio F S  /F A  of the output frequencies of the respective second and first oscillators does not substantially depart from unity within the output frequency range and the product of the second division factor Q by the standard frequency is of the same order of magnitude as the arithmetical mean of the lower and upper limits of said predetermined output frequency range. 
     
     
       3. A frequency synthesizer as claimed in claim 1, wherein said output means of the third frequency divider includes an harmonic generator. 
     
     
       4. A frequency synthesizer for generating an output frequency variable in a predetermined range by frequency steps having a predetermined value, said synthesizer comprising a first phase locked loop including a first current or voltage controlled oscillator, said first oscillator having a frequency control input and an output, a first phase comparator having first and second inputs and an output, the output of the first comparator being connected to the frequency control input of the first oscillator, source means providing an input frequency (F o  +Δ), F o  being a fixed frequency and Δ being a frequency increment variable by predetermined steps which are small with respect to the steps of variation of the output frequency; first divider means connecting said source means to the first input of the first comparator, said first divider means having a first programmable division factor N which is adapted to take a first number of values equalling the number of steps of variation in said output frequency range; second divider means and first mixer means serially connected between the output of the first oscillator and the second input of the first comparator, said second divider means having a second predetermined factor of division Q and a source of standard frequency connected to the first mixer means, said frequency synthesizer further comprising a second phase locked loop including a second current or voltage controlled oscillator having a frequency control input and an output on which the output frequency of the synthesizer is generated, a second phase comparator having first and second inputs and an output, the output of the second phase comparator being connected to the frequency control input of the second oscillator; second mixer means having first and second inputs and an output, the first and second inputs of the second mixer means being respectively connected to the respective outputs of the first and second oscillators, and circuit means connecting the output of the second mixer means to the first input of the second phase comparator and the output of the first oscillator to the second input of the second phase comparator, said circuit means comprising a third frequency divider having a third predetermined division factor R, an input connected to the output of said first oscillator and output means connected to the second input of the second comparator, and means connecting the output of the second mixer means to the first input of the second comparator, the first and second factors N and Q and the standard frequency having such values that the output frequency F A  of the first oscillator is located within the predetermined range of the output frequency, said output means of the third frequency divider comprising a first harmonic generator, said circuit means further comprising at least one further mixer means having a first input connected to the output of the second mixer means and an output connected to the first input of the second comparator, said further mixer means having a second input, at least one further divider having a further predetermined factor R 1  and an input connected to the output of the first oscillator and an output, and at least one further harmonic generator connecting the output of the further divider to the second input of the further mixer means. 
     
     
       5. A frequency synthesizer for generating an output frequency variable in a predetermined range by frequency steps having a predetermined value, said synthesizer comprising a first phase locked loop including a first current or voltage controlled oscillator, said first oscillator having a frequency control input and an output; a first phase comparator having first and second inputs and an output, the output of the first comparator being connected to the frequency control input of the first oscillator, source means providing an input frequency (F o  +Δ)/Q, F o  being a first frequency and Δ being a frequency increment variable by predetermined steps which are small with respect to the steps of variation of the output frequency and Q being a second predetermined factor; first divider means connecting said source means to a first input of the first comparator, said first divider means having a first programmable division factor N which is adapted to take a first number of values equalling the number of steps of variation in said output frequency range; first mixer means connected between the output of the first oscillator and the second input of the first comparator, and a source of standard frequency connected to the first mixer means, said frequency synthesizer further comprising a second phase locked loop including a second current or voltage controlled oscillator having a frequency control input and an output on which the output frequency of the synthesizer is generated, a second phase comparator having first and second inputs and an output, the output of the second phase comparator being connected to the frequency control input of the second oscillator; second mixer means having first and second inputs and an output, the first and second inputs of the second mixer means being respectively connected to the respective outputs of the first and second oscillators, and circuit means connecting the output of the second mixer means to the first input of the second phase comparator and the output of the first oscillator to the second input of the second phase comparator, said circuit means comprising a further frequency divider having a third predetermined division factor R, an input connected to the output of said first oscillator and output means connected to the second input of the second phase comparator, and means connecting the output of the second mixer means to the first input of the second phase comparator, the first and second factors N and Q and the standard frequency having such values that the output frequency F A  of the first oscillator is located within the predetermined range of the output frequency. 
     
     
       6. A frequency synthesizer for generating an output frequency variable in a predetermined range by frequency steps having a predetermined value, said synthesizer comprising a first phase locked loop including a first current or voltage controlled oscillator, said first oscillator having a frequency control input and an output, a first phase comparator having first and second inputs and an output, the output of the first comparator being connected to the frequency control input of the first oscillator, source means providing an input frequency (F o  +Δ), F o  being a fixed frequency and Δ being a frequency increment variable by predetermined steps which are small with respect to the steps of variation of the output frequency; first divider means connecting said source means to the first input of the first comparator, said first divider means having a first programmable division factor N which is adapted to take a first number of values equalling the number of steps of variation in said output frequency range; second divider means and first mixer means serially connected between the output of the first oscillator and the second input of the first comparator, said second divider means having an output and a second predetermined factor of division Q and a source of standard frequency connected to the first mixer means, said frequency synthesizer further comprising a second phase locked loop including a second current or voltage controlled oscillator having a frequency control input and an output on which the output frequency of the synthesizer is generated, a second phase comparator having first and second inputs and an output, the output of the second phase comparator being connected to the frequency control input of the second oscillator; second mixer means having first and second inputs and an output, the first and second inputs of the second mixer means being respectively connected to the respective outputs of the first and second oscillators, and circuit means connecting the output of the second mixer means to the first input of the second phase comparator and the output of the second divider means to the second input of the second phase comparator, said circuit means comprising a third frequency divider having a third predetermined division factor R, an input connected to the output of said second divider means and output means connected to the second input of the second comparator, and means connecting the output of the second mixer means to the first input of the second comparator, the first and second factors N and Q and the standard frequency having such values that the output frequency F A  of the first oscillator is located within the predetermined range of the output frequency, said output means comprising at least one further mixer means having a first input connected to the output of the second mixer means and an output connected to the first input of the second comparator, said further mixer means having a second input and at least one harmonic generator connecting the output of the second divider means to the second input of the further mixer means. 
     
     
       7. A frequency synthesizer as claimed in claim 4, wherein said circuit means further comprise filter means serially interconnecting the respective second and further mixer means and the second comparator and wherein the algebraic sum Σ of the quotients by the respective ranks of the harmonics generated by the respective first and further harmonic generators by the respective fixed division factors R and R 1  of the third and further divider means is so predetermined that the ratio (1+Σ)/N is a constant proportional to the quotient of said predetermined value of the frequency step of the output frequency by the standard frequency.